On Jun 12, 2012, at 10:47 PM, Masataka Ohta wrote: > Dave Hart wrote: > >> It is >> not transparent when you have to negotiate an inbound path for each >> service. > > I mean, for applications, global address and global port > numbers are visible. >
Showing that you don't actually understand what everyone else means when they say "end-to-end". >> UPnP >> is inadequate for carrier NAT due to its model assuming the NAT trusts >> its clients. > > UPnP gateway configured with purely static port mapping needs > no security. > > Assuming shared global address of 131.112.32.132, TCP/UDP port > 100 to 199 may be forwarded to port 100 to 199 of 192.168.1.1, > port 200 to 299 be forwarded to port 200 to 299 of 192.168.1.2, > ... > No carrier is going to implement that for obvious reasons. Besides, that's not transparent end-to-end, that's predictably opaque end-to-end. >> When TCP headers are being rewritten, it's a strong hint that >> transparency has been lost, even if some communication remains >> possible. > > UPnP provides information for clients to restore IP and TCP > headers from local ones back to global ones, which is visible > to applications. > But it doesn't work across multiple layers of NAT. > See the following protocol stack. > > UPnP capable NAT GW Client > +---------+ > | public | > | appli- | > | cation | > information +---------+ > +------+ for reverse translation | public | > | UPnP |-------------------------->|transport| > +---------+---------+ +---------+ > | public | private | | private | > |transport|transport| |transport| > +---------+---------+ +---------+ +---------+ > | public | private | | private | | private | > | IP | IP | | IP | | IP | > +---------+-----------------------+-----------------------+ > | privatte datalink | private datalink | > +-----------------------+-----------------------+ Now, redraw the diagram for the real world scenario: host <-> UPnP NAT <-> Carrier NAT <-> Internet <-> Carrier NAT <-> UPnP NAT <-> host Tell me again how the application signaling from UPnP survives through all that and comes up with correct answers? Yeah, thought so. Owen
